I have been researching this same issue for a few months, waiting to upgrade the factory CD changer on my 2005 Sequoia Limited.
I started by noticing that a lot of people have Pioneer Avic systems. After reading more, and watching a ton of videos and reading endless forums...I started drifting over to Kenwood. I've pretty much made up my mind on the Kenwood dnx 6960. It's got 5V outputs (important for our JBL Sequoia amps), also it doesn't need a separate module for sirius (just a cable CA-SR20V). It uses Garmin Navigation which is the best in my opinion. I like the dedicated volume knobs. It supports a backup camera (CCD-2000). Finally, it interfaces with the Sequoia steering wheel controls (PAC SWI-JACK).
Don't get me wrong...the Pioneer and Eclipse models are also pretty amazing and can do all of these things. It's just that the combination of Garmin Nav and reliability that I've seen dealers write about make the Kenwood better in my opinion. Price is also pretty low on Amazon. my 2cents!